     [civs.logic.demographics :refer :all])
   (:import [civs.model.core Population Tribe]))
 
+(def migration-radius 3)
+
 (defn chance-to-become-semi-sedentary [game tribe]
   (let [ world (.world game)
          prosperity (prosperity game tribe)]

      (let [ world (.world game)
             pos (.position tribe)
             sp (split-pop (.population tribe))
             possible-destinations (filter #(pos-free? game %) (land-cells-around world pos 3))
             preferences (map (fn [pos] {
                                          :preference (perturbate-low (prosperity-in-pos game tribe pos))
                                          :pos pos

      (let [ world (.world game)
             pos (.position group)
             _ (check-valid-position world pos)
             possible-destinations (filter #(pos-free? game %) (land-cells-around world pos migration-radius))
             preferences (map (fn [pos] {
                                     :preference (perturbate-low (prosperity-in-pos game group pos))
                                     :pos pos
